Process of tanning hides



Patented'Aug. 14, 1934 UNITED STATES PATENT OFF ICE PROCESS OF TANNING HIDES Max Bergmann, Dresden, Germany No Drawing. Application July 28, 1933, Serial No. 682,632. In Germany August 1, 1932 7 Claims.

whereupon the iron-tanned leather thus obtained is further dressed with the aid of another mineral tanning material, such as chrome' aluminiumand the like tanning material. The albuminoid substances employed for the production of the tanning agent used for the first phase of this combined tanning process have partly been hydrolyzed, but-they have also been changed in other respects by the oxidizers, thus forming with the iron a combination which exercises the tanning effect aimed at in this instance.

By treating the hides with the ferro-albuminoid tanning agents a leather is obtained which is characterized by an excellent grain and good filling, thus differing advantageously also from the ordinary iron-tanned leather. By subsequently treating the leather thus obtained with mineral tanning agents, a filling and a body or state of the leather are secured which are quite exceptional with mineral leathers of any other description. It is a surprising'fact, that in spite of this excellent filling also the condition of the so-called fattening folds is a very favourable one, and even the inferior or depending parts of the hide presentin this leather a very favourable appearance, such as has been impossible .to obtain with the aid of the combined tanning processes known so far. The spu'ial advantages of the leather thus obtained render. it possible to employ it for uppers, well as for soles and other purposes. The leather is distinguished by a light, uniform colour, for which reason it is also highly suitable for producing coloured leather.

The possibility of subsequently tanning and filling the leather, which has previously been tanned with a ferruginous tanning agent, with copious quantities of other mineral tanning agents is given by the fact, that as ierruginous tanning agent one of such nature isv employed which contains albuminoid substances oralbumi-' noid waste products in complex combination. It is by this fact that the leather tanned therewith obtains the property, in spite of having already been tanned through, of absorbing further considerable quantities of other mineral tanning agents ensuring in this way the effect indicated above. For this reason it is important, that the treatment of the leather with chrome tanning agents or the like is effected only after previous treatment with the ferruginous albuminoid tanning agents and not vice versa.

- All mineral tanning agents are to be considered for the subsequent additional tanning process, e. g. the customary chrome tanning agents.

Examples of performance (1) For the purpose oi. tanning 500 kilos of true skins or depilated hides, which have previously been slackened, unlimed and, if necessary, bated and pickled, an albuminoid tanning solution is prepared containingabout 3% of FezOa reckoned on the weight of the employed true skins. An advantageous way for obtaining thisferruginous albuminoid tanning agent consists in heating 5'.) kilos of chrome shavings or other leather or skin waste, which may also be replacedby the corresponding quantity of parings of skins or scraps of hide or any other albuminoid product, together with an iron salt obtained from 10 kilos'of scrap iron,- eg. ferricchloride, and with 100 kilos of nitric. acid of 22 B., during some time to -90' C. until total solution has taken place. After cooling this tanning solution is neutralized with a 10% sodium carbonate solution to such an extent that its pH-value equals about 2.

With the aid of this solution which may, if necessary, yet be diluted, the tanning of the true skins is now effected in the vat or suspension tub in the usual manner until the skins are properly bitten through or, in other words, fully permeated by the tanning solution. The skins then are further tanned through while further quantities of sodium carbonate are added until the tanning solution has attained a pH-value of about 4 and the separation of iron in a flocculent state yet remains just avoided, which will be the case after 6 to 8 hours, if the tanning process takes place in the vat.

After the skins thus treated have been beaten over the jack for sometime, they are tanned a .second time with chrome compounds. For this purpose they are suitably fulled for 1 to 2 hours in a chrome-alum solution, containing 2 to 3% of CrzOa related to the weight of the true skins employed and having a basicity of about The skins then are stored for 1 to 2 days and hereafter neutralized with .5% of sodium bicarbonate. They are subsequently washed, greased and dressed in accordance with known methods. Borax, as well as water-glass, may also be used as neutralizing agents, the water-glass imparting to the leather a particularly attractive light colour.

The described process may also be altered in such a way that the leather, treated with the i'erruginous albuminoid taming agent is neutralized first and subsequently tanned with a strongly basic chrome liquor.

(2) For the prepartion oi the tanning solution to be used in the first stage of the tanning process, 50 kilos of shavings or the corresponding quantity of scraps oi hide, glue or the like are heated with 50 kilos of iron chloride and 150 liters of 18% hydrochloric acid to about 80 to 90 C. until the mass will be fully dissolved. In order to oxidize the iron salt, for instance 20 kilos of potassium chlorate then are gradually added to the solution, which is further heated until the reaction is completed. This will be the case when the Irothing has ceased. The solution thus obtained will sufiice for the treatment of j 500 kilos of true skins, if it is intended to tan with 3% of F8203 reckoned on the weight 01 the true skins employed. The solution is made up in the manner described in Example 1 with a sodium carbonate solution of 10% contents to an approximate pH value or 2, and the tanning then is effected in a corresponding manner. The subsequent second tanning with chrome tanning agents here also will be effected in the manner indicated in Example 1.

If desired, the subsequent second tanning with the chrome tanning agents or the like may also be effected without previous neutralization of the leather preliminarily tanned with iron compounds. I

(3) Instead oi the subsequent second tanning being performed by means of chrome compounds, aluminium compounds may also be employed for this purpose. In this case the leathers, after having completed the iron tanning process described, are fulled with 50 kilos of alum or with the corresponding quantity oi aluminium sulphate and 100% of water. By gradual addition of a 10% solution of sodium carbonate, the basicity of the solution is gradually raised until the point of fiocculent separation of the aluminium is nearly attained. After iulling the skins for 1 to 1 hours, the second stage of the tanning process will be completed. The leathers are then washed, neutralized it necessary. greased and dressed in accordance with customary methods.

The leathers treated with alum are of a very nice light colour and are distinguished by anexcellent feel or touch and very good filling or preparing the tanning liquor for the first stage of the process, such as shavings of vegetably tanned leather, glue casein, waste of artificial albuminoid masses, horn, hairs, for instance calts hairs, and decomposition products of such substances. A contents of tanning substances oi the shavings or other leather waste does not adversely influence the process, but also is not decisive for itasuccess. 1

Instead of nitric acid or potassium chlorate other oxidizing means, such as nitric oxides, free chlorine, potassium permanganate and the like may be used for the preparation of the ferroalbuminoid tanning agent.

Having now particularly described and ascertained the nature. of my said invention, I declare that what I claim is; I

I 1. A process of tanning hides,- conslsting in the hides first are tanned with a solution obtained by, the treatment of albuminoid substances with acids and oxidizing means in the presence of iron salts, whereupon they are tanned a second time with other mineral tanning agents.

2. A process of tanning hides, consisting in the hides first are tanned with a solution obtained by the treatment of albuminoid substances with acids and oxidizing means ,in the presence of iron hides first are tanned with a solution obtained by the treatment of albuminoid substances with acids and nitrogen-oxygen compounds in the presence of iron salts, whereupon they are tanned a second time with other mineral tanning agents.

5. A process of tanning hides, consisting in the hides first are tanned with a solution obtained by the treatment of albuminoid substances ,with

nitric acid in thepresence of iron salts, whereupon 123 they are tanned a second time with other mineral tanning agents.

6. A process of tanning hides, consisting in the hides first are tanned with a solution obtained by the treatment of albuminoid substances with 125,

acids and a nitric oxide in the presence of iron salts, whereupon they are tanned a second time with other mineral tanning agents.

7. A process of tanning hides, consisting in the hides first are tanned with a solution obtained by the treatment of albuminoid substances with acids and chlorates in the presence of iron salts, whereupon they are tanned a second time with other mineral tanning agents.

MAX BERGMANN. 

